DESCRIPTION: The identification of genetic alterations implicated in the pathogenesis and progression of specific cancers raises the interest in the development of novel genetic targeting strategies that may eventually lead to new approaches for cancer therapy. The overall goal of the proposed research is to determine whether triplex forming oligonucleotides (TFOs) can selectively target and permanently inactivate oncogenes in cancer cells. TFOs may block DNA replication at selected sites in a target gene ad induce mutations or deletions at the site of replication fork arrest. Targeted mutations in either the regulatory or coding region of a gene would prevent transcription of the gene or result in the production of an inactive mRNA or protein. Furthermore, cancer cells may be more sensitive than normal cells to a TFO-induced gene damage because of their intrinsic genetic instability. The proposed studies have the following Specific Aims: 1) to determine the cellular and nuclear uptake of TFOs and triplex DNA formation at the specific sites in either the c-myc, cyclin D1, or erb B2/neu gene in normal and cancer cells; 2) to determine the effects of TFOs on replication fork progression in the target genes; 3) to determine whether TFOs induce mutations or deletions in the target genes and inhibit gene expression; 4) to determine the effects of oncogene-targeted TFOs on proliferation of normal and cancer cells. It is anticipated that the results of the proposed studies will provide important insights into the mechanism of action of TFOs and on the potential of TFOs as gene targeting agents. These findings may open new perspectives for the use of TFOs in cancer therapy.